There are numerous applications for radar devices in various fields of industry. For example, the use of radar sensors is possible for short-range sensors in motor vehicles.
Essentially, a transmitting antenna in such radar devices emits electromagnetic waves. When these electromagnetic waves strike an obstacle, they are reflected and received by another antenna or the same antenna after being reflected. The received signals are then sent to a signal processing and analyzing unit.
In motor vehicles, for example, radar sensors are used for measuring the distance from targets and/or the relative velocity with respect to such a target outside the motor vehicle. Targets include, for example, parked vehicles or vehicles driving in front, pedestrians, cyclists or devices in the vicinity of the vehicle.
FIG. 1 is a schematic block diagram of a radar device having a correlation receiver according to the related art. A transmitter 300 is prompted by a pulse generator 302 to send a transmission signal 306 over antenna 304. Transmission signal 306 also strikes a target object 308, where it is reflected. Reception signal 310 is received by antenna 312. This antenna 312 may be identical to antenna 304. After receiving reception signal 310 by antenna 312, the signal is sent to receiver 314 and then supplied over a unit 316 having a low-pass filter and analog-digital converter to a signal analyzer 318. The special feature of this correlation receiver is that receiver 314 receives a reference signal 320 from pulse generator 302. Reception signals 310 received by receiver 314 are mixed with reference signal 320 in receiver 314. Using the correlation it is possible to determine, for example, the distance of a target object on the basis of the time lag from sending to receiving the radar pulses.
With ordinary pulsed radar devices, both the mid-frequency and the pulse repetition frequency are preselected as fixed frequencies. In particular in conjunction with special approval regulations, these fixed preset quantities may result in unacceptably high levels. Likewise, such devices are highly sensitive to interference.